Polyacrylonitrile synthetic fiber and a process of manufacturing the same

ABSTRACT

AN ACRYLONITRILE SYNTHETIC FIBER HAVING A FUR-LIKE CONFIGURATION, TOUCCH AND FEELING TO THE HAND, IS COMPOSED OF A THICKER MIDDLE PORTION AND FINER TAPERING PORTIONS WHICH EXTEND FROM THE THICKER MIDDLE PORTION AND HAVE A LENGTH LONGER THAN TEN TIMES THE AVERAGE DIAMETER OF THE   THICKER MIDDLE PORTION AND AN AVERAGE DIAMETER SHORTER THAN HALF OR THE AVERAGE DIAMETER OF THE THICKER MIDDLE PORTION AND HAVE NUMEROUS ASYMMETRICAL RIDGES ON ITS SURFACE.

5, 1974 ZEN-ICHI ORITO ETAL 3,827,932

. POLYACRYLONITRILE SYNTHETIC FIBER AND A PROCESS OF IANUFA'CTURIHG TEE SHE Filud July 13, 1971 2 Sheets-Sheet 1 Aug; 1974 ZEN-ICHI ORITO ETAL 27,

POLYACRYLONITRILE SYI'THETIC FIBER AND A PROCESS OF "ANUFACTURING THE SAIE mm July 15, 1971 I 2 Sheets-Sheet 2 MAXIMUM RESISTANCE PULL OUT RESISTANCE I9) PULL OUT DISTANCE (cm) United States Patent Oflice 3,827,932 Patented Aug. 6, 1974 tis. Cl. 161-172 7 Claims ABSTRACT OF THE DISCLOSURE An acrylonitrile synthetic fiber having a fur-like configuration, touch and feeling to the hand, is composed of a thicker middle portion and finer tapering portions which extend from the thicker middle portion and have a length longer than ten times the average diameter of the thicker middle portion and an average diameter shorter than half of the average diameter of the thicker middle portion, and have numerous asymmetrical ridges on its surface.

. The present invention relates to an improved acrylonitrile synthetic fiber and a process of manufacturing the same, and more particularly, relates to an improved acrylonitrile synthetic fiber having tapering end portion and ridges formed on the fiber surface and having directionality in frictional property and a process of manufacturing the same.

While acrylonitrile synthetic fibers are widely used in various fields of knitted, woven and non-woven fabrics, especially, knitted fabric owing to its good physical propties, some consumers dislike the acrylonitrile synthetic fiber because of its special hand feeling different from that of natural fibers. Accordingly, many attempts have been made to impart the desired hand feeling similar to that of the natural fibers, especially, wool. For example, an acrylonitrile synthetic fiber having a special crimping property has been prepared by side-by-side type conjugate spinning process or other processes. However, while the conjugate acrylonitrile synthetic fiber has a crimping property and appearance resembling that of wool, it does not have the high resiliency, softness, and slimness similar to wool. All such attempts have so far failed to accomplish the purpose.

This is due mainly to the fact that the fur fibers have a special configuration different from that of the ordinary crimp synthetic fibers.

It is known that the fur fibers have scale-like ridges known as serrations having directionality in frictional property, on the surface thereof.

Further, it is an important feature that the cross-sectional area of the fur fibers varies along the length thereof and the end portion of the fiber tapers. This special configuration is characteristic of the fur fibers and close-.

ly relates to the touch and hand feeling thereof.

Compared with the fur fibers, the acrylonitrile synthetic fibers are stretched in only a longitudinal .direction of the fiber throughout the spinning and drawing process. Accordingly, the striations formed on the fiber surface extend parallel to the longitudinal axis of the fibers so as to form linear strips which do not resemble the serrations of the fur fibers. Further, when the acrylonitrile synthettic fibers are cut into staple fibers in the conventional manner, the crosssectional area of the middle portion of the fibers is substantially equal to that of the end portion and therefore the end portibn is not tapered.

Therefore, in order to obtain acrylonitrile synthetic fiber having the touch and hand feeling resembling those of good quality fur, it is necessary that the acrylonitrile synthetic fiber has the serration-link ridges having directionality on the surface and terminates with the end portion tapering.

An object of the present invention is to provide an improved acrylonitrile synthetic fiber having a special configuration, touch and hand feeling similar to those of fur, and a process of manufacturing the same.

The acrylonitrile synthetic fiber of the present invention is composed of a thicker middle portion and finer tapering end portions extending from the middle portion and having dimensions satisfying the following relationships:

L/D 10 and d 0.SD

wherein D represents an average diameter in ,u of the middle portion, d represents an average diameter in p of the tapering end portion and L represents a length in ,u. of the tapering end portion, and provided with asymmetrical ridges outwardly projecting from the fiber surface.

The acrylonitrile synthetic fiber according to the present invention is manufactured by the process in which an acrylonitrile synthetic filament having a fineness periodically varying along the length of the filament is prepared from a polymer comprising acrylonitrile as a main component, the filament is draft-cut into a staple fiber, the staple fiber thus prepared is insolubilized at the surface so that it does not dissolve in dimethyl formamide at a temperature of 75 C. The insoluble outer layer at the thicker middle portion has a cross-sectional area of 2 to 40% based on the whole cross-sectional area at the thicker middle portion, and the insolubilized staple fiber is treated with an aqueous solution containing an organic solvent or mixture of organic solvent and inorganic salt as specified hereinafter, whereby the staple fiber is shrunk thus forming the directional ridges on the fiber surface.

These and other features of the present invention will be more apparent from the following description and the accompanying drawings, in which FIGS. 1 and 2 are scanning type electron microscopic photographs showing the surface of the acrylonitrile synthetic fiber of the present invention,

FIG. 3 is a graph showing a relationship between pullout resistance and pull-out distance when a fiber is pulled out from a fiber bundle, and

FIG. 4 is a schematic view of an embodiment of an apparatus for manufacturing a filament having periodically varying fineness.

The special configuration of the acrylonitrile synthetic fiber of the present invention is clearly illustrated in FIGS. 1 and 2. FIG. 1 shows a secondary electron image of the surface of the tapering end portion of the fiber which image is emitted from the fiber surface by direct line scanning of the primary electron beam onto the fiber surface. FIG. 2 shows an enlarged secondary electron image of the surface of a part of the fiber at which the diameter of the fiber begins to decrease. As is clearly shown in the drawings, the acrylonitrile synthetic fiber of the present invention has numerous ridges formed on the fiber surface. The interval, height and shape of the ridge are calculated from the secondary electron image obtained by positioning the fiber at right angles to the primary electron beam and taking the focus on both sides of the fiber (upper and lower parts of the thickest portion of the image shown in FIGS. 1 and 2).

' ing from 0.2 to 1.5,u, more preferably, from 0.3 to 1.0g.

I It is important that the cross-section of the ridges taken "atright" angle 'to' the face of'the ridge alo'nglh' rouge"- directional selectivity in frictional resistance, more concretely, refers to the property that the frictional resistance when a fiber is pulled out from a fiber bundle in toroot direction (counter-direction) of the ridge on thelfiber surface is higher than the frictional resistance when .a fiber is pulled out from the fiber bundle in root-to tip direction (co-direction) of the ridge on the surface. Detailed explanation of method for measuring the directionality in frictional resistance is given in the Journal of the Textile Institute, Vol. 37, T269 (1946).

Referring to FIGS. 1 and 2 once again, the cross-section of the ridges taken at right angle to the face of the ridge along the longitudinal axis of the fiber is asymmetrical about the center line of the ridge. That is, the ridges outwardly project in a direction inclined toward the stretching direction of the fiber during spinning and drawing process. The stretching direction is shown by arrow in FIGS. 1 and 2.

When a fiber is pulled out from a fiber bundle in which numerous fibers are laid in the same direction with respect to the stretching direction, the pull-out resistance changes with the pull-out distance as shown in FIG. 3. The curve in FIG. 3 shows that the relationship between the pull-out resistance and distance, has a peak point. The peak refers to maximum frictional resistance. The maximum frictional resistance of the fiber when the fiber is pulled out in codirection 'with respect to the stretching direction is lower than that in the counter-direction.

The ratio of the maximum frictional resistance in counter-direction with respect to that in co-direction is in a range from 1.3 to 3.0. This ratio range is very approximately that of natural fur.

The acrylonitrile synthetic fiber of the present invention is composed of a thicker middle portion and finer tapering end portions extending from the middle portion. The thicker middle portion contributes to the high rigidity and resiliency of the product made up of the fibers of the present invention, and the finer tapering end portion to high soft touch and hand feeling of the product. Accordingly, the product has a high resiliency and a very soft touch.

The acrylonitrile synthetic fiber of the present invention may be prepared from a polymer comprising acrylonitrile unit as a main component, more concretely, polyacryloni-trile, or copolymers of at least 85% by weight of acrylonitrile with at most 15% by weight of other vinyl or vinylidene monomer, for example, methyl acrylate, methyl methacrylate, vinyl acetate, vinyl chloride and vinylidene chloride, by the conventional wet or dry spinning process.

Generally, the pointed or "tapering fiber is manufactured by periodically varying the fineness of the continuous filament in spinning or drawing process, and draft-cutting the continuous filament at finer portions thereof into staple fibers so that the end portions of the staple fibers are tapered.

The periodical varying of the continuous filament fineness, is effected in the following manner.

(I) Periodically varying the output of the spinning tion through the spinning orifice. (2) Periodically varying the stretch ratio of the filament in the spinning or drawing process while stretching the filament by intermittently impacting the filament as it continuously runs through an impacting device so as to partially draw the filament at a high draw ratio. (3) Periodically varying the drawing property (plasticity) of the filament while stretching the filament "by in p termittently heating the filament as it continuously runs soluthrough a heating device such as heating pin so as to "pa'rtiany draw tlie'filament at a higherdraw'ratio.

The continuous filament having the periodically varying fineness is draft cut at its finer portion into pointed or tapering staple fibers by using a perlock system, tarbo stapler or other drawing machines. v p The tapering fibers thus prepared are partiallyinsolubilized to solvent for, the acrylonitrile polymer or copolymers by treating them with an insolubilizing agent such as described hereinafter, and then shrunk with a shrinking -agent. By the above treatments, numerous asymmetrical ridges are formed on the fiber surface.

In a preferred embodiment of the process of producing the tapering fiber, a spinning solution of an-acrylonitrile polymer or copolymer is extruded through a spinneret and coagulated into filament form, the filament is intermittently impacted while running through coagulating or drawing apparatuses so as to periodically vary the stretch ratio of the filament, and the filament of which fineness periodically varies along its length by the "a'bove intermittent impacts is draft-cut at the finer portions there'of into staple fibers having tapering end portions.

.An embodiment of apparatus for effecting the above process is shown in FIG. 4. Referring to FIG. 4, a spinning solution A is extruded into a coagulating liquid 2 in a bath 3 through a feeding conduit 1' and spinneret 4 and coagulated into a filament form. The filament 5 thus obtained is withdrawn from the coagulating liquid 2 and advanced through guides 6 and 7 and rollers '8, 9, 10 and 11 to a Winding roller (which is not illustrated in the drawing). A device 20 for intermittently impacting the filament is located between the guides 6 and 7.

The device 20 comprises a rotation shaft 21 connected to a driving motor (which is not illustrated in the drawing), an eccentric cam 22 connected with the rotation shaft 21, a slide ring 23, a bearing 24 inserted between the eccentric cam 22 and slide ring 23, a piston rod 25 connected with the slide ring 23 and a supporter 26 for the piston rod 25. Whenthe rotation shaft 21 rotates together with the eccentric cam 22 at a predetermined rotation rate, the slide ring 23 moves up and down as indicated by arrows in the drawing, and therefore, the piston rod 25 moves up and down, whereby the filament 5 is periodically impacted between the guides 6 and 7 by the bottom end of the piston rod 25.

When the filament 5 is impacted by the piston rod 25, the filament 5 is bent as shown in the drawing, whereby the filament path is extended and the stretch ratio of the filament 5 is enlarged so as to lower the fineness of thefilament 5.

Through the above-mentioned intermittent impacts, the fineness of the filament periodically varies.

It is observed that when a filament bundle of a total thickness of at least about 30,000 denier is processed by utilizing the intermittently impacting device of FIG. 4, the formed finer portions of the filaments-are distributed at random in the filament bundle. While" the reason for this phenomenon is not clear as yet, a supposition is that the very large total thickness of the filament bundle causes non-uniform removal of the solvent from the spinning solution in the coagulating step or non-uniform'heating of the filament bundle in the drawingtstep, and the non-uniformity of the filament results in the fact that the drawing points of the filament in the bundle are distributed at random in the bundle.

The filament bundle thus produced is draft-cut into tapering staple fibers by a conventional draft-cutting machine such as perlock system and tarbo stapler.

- The tapering acrylonitrile synthetic fiber of the present invention is required to satisfy the following relationships:

However, in the process of the present invention ,the

The requirement that the acrylonitrile synthetic fiber of the present invention must have the above stated tapering configuration derives from the fact that good quality fur fibers such as lamb, angora, and merino wools satisfy the above relationships and even when the animals are subjected to repeated cutting, the cut wool contains considerable amounts of newly grown wool satisfying the above relationships.

The tapering acrylonitrile synthetic fiber is insolubilized at its surface by treating it with an insolubilizing agent, so that its outer layer is insoluble in dimethyl formamide at a temperature of 75 C. The insolubilized tapered fiber is, next, subjected to shrinking treatment using an aqueous solution of an organic solvent or of mixture of organic solvent and inorganic salt in order to form the ridges on the fiber surface. The ridges are formed because of the following. That is, through the insolubilization of the fiber at the surface the structure of the fiber changes to a different phase structure resembling the so-called skin-core structure. The outer layer is insolubilized to dimethyl formamide which is a solvent for the acrylonitrile polymer or copolymers. Accordingly, when the fiber is treated with the shrinking agent, the degree of swelling of the outer layer is lower than that of the core portion, and therefore, the core portion shrinks at a shrinkage greater than that of the outer layer. This uneven shrinkage of the fiber results in the formation of numerous ridges on the fiber surface.

It is important that the ridges formed on the thicker middle portion of the acrylonitrile synthetic fiber of the present invention are asymmetric similar to those of the natural fur fibers so as to give directionality in frictional resistance of the fiber.

Generally, the ridges on the finer portion of the fiber tend to have a height lower than that of the thicker portion owing to the fact that a ratio of cross-sectional area of the insoluble outer layer of the finer portion with respect to whole area of this portion is higher than that of the'thicker portion, and therefore, the shrinkage of the finer portion is lower than that of the thicker portion. However, the height of the ridges on the finer portion can be adjusted by adjusting the cross-sectional area of the insoluble outer layer.

It is preferable for forming the desirable ridges on the fiber surface that the cross-sectional area of the insoluble outer layer of the thicker middle portion is in a range from 2 to 40%, more preferably, 5 to 30% with respect to the whole cross-sectional area of this portion.

It is known that the coating layer applied onto the acrylonitrile synthetic fiber surface and consisting of a substance insoluble to dimethyl formamide can not be converted to ridges having the directionality in frictional resistance. Therefore, it is supposed that the formation of the asymmetrical ridges is derived from the internal deformation of the fiber during spinning and drawing steps.

The height and interval of the ridges can be adjusted by controling the conditions of the insolubilizing process and the shrinking process.

The tapering fiber of the present invention perferably has ridges having a height ranging from 0.2 to 1.5 and directionality in frictional resistance on the surface of the thicker portion thereof.

The insolubilizing of the acrylonitrile synthetic fiber may be effected by saponification using aqueous solutions of hydroxides of sodium, potassium and lithium or sulfuric acid, or by other chemical reaction using aqueous solution of hydrazine salts or hydroxyl amine salts. These reactions are eifected successively from the outside surface to inside portion of the fiber. Accordingly, it is possible that only the outer layer is insolubilized and the core portion remains in a soluble condition.

In order to form the ridges on the fiber surface, the fiber is treated with an aqueous solution of organic solvent or mixture of the organic solvent and inorganic salt.

The organic solvent may be selected from the group consisting of alkylene carbonates having 3 to 5 carbon atoms such as ethylene carbonate, propylene carbonate, trimethylene carbonate, tetramethylene carbonate, and 2,3-butylene carbonate; -butyrolactone; a-valerolactone; and maleic acid anhydride. The inorganic salts may be selected from salts having a solubility of 100 g./l. or higher in water at a temperature of 70" C., preferably, halogenated compounds, rhodanates, sulfates, phosphates and nitrates of alkali metals, zinc, aluminum, manganese and ammonium. Especially, the sulfates of the alkali metals and ammonium are highly effective for lowering the content of the organic solvent necessary in-order that the shrinking liquid has the desired shrinking effect, and for preventing the fibers from undesirably adhering to each other during the shrinking treatment.

The shrinking treatment may be performed by treating the fiber in an aqueous shrinking solution heated to a high temperature or by impregnating the fiber with an aqueous shrinking solution, and then heating it to dry.

When the fiber is treated in the high temperature shrinking solution, the required amount of the carbonate compound varies corresponding to the temperature and content of the inorganic salt. If the inorganic salt is not added to the shrinking solution, it is necessary that the content of the carbonate compound is 15 to 40% by weight, and when the neutral salt is added, the content of the carbonate compound may be as low as 3% by weight. Since the outer layer of the fiber is insoluble, the shrinking treatment can be effected in a favorable condition with no adhering of the fibers to others even when the content of the organic solvent in the shrinking solution is so high that the regular acrylonitrile synthetic fiber is dissolved therein.

In order that the shrinking treatment is sufiieiently effected in the high tempeeature shrinking solution, it is necessary that the temperature of the solution is 70 C. or higher. In order that the shrinking treatment is sufliciently effected by the impregnating-heating method, it is required that the heating temperature is C. or higher. In this case, the amount of the carbonate adhered to the fiber is preferably 3 to 15% based on the weight of the dried fiber.

Owing to the fact that the acrylonitrile synthetic fiber of the present invention is provided with the ridges having directionality in frictional resistance on its surface and the fiber is terminated by the tapering end portion, the products made up from the tapering fibers have a high resilience and soft hand touch different from those of the products made from the conventional acrylonitrile synthetic fibers.

The tapering acrylonitrile synthetic fiber of the present invention may be utilized for manufacturing various products. The tapering fibers may be blended with other synthetic fibers or natural fibers. In both utilizations, the features of the tapering fiber of the present invention is effective for creating the excellent quality of the product.

Example 1 A spinning solution was prepared by dissolving 23.5 parts by weight of an acrylonitrile copolymer which consists of 93% by weight of acrylonitrile and 7% by weight of vinyl acetate and has a degree of polymerization of 1500, into 76.5 parts by weight of dimethyl acetamide. The spinning solution was extruded into a coagulating liquid of a temperature of 50 C. consisting of 55 parts by weight of dimethyl acetamide and 45 parts by weight of water through a spinneret having 40,000 orifices of 0.08 mm. diameter to form filaments. The coagulated filaments were withdrawn from the coagulating liquid and then fed to an intermittently impacting device as shown in FIG. 4. The device was disposed between two guides spaced at 60 cm. and had a reciprocal piston rod. The piston rod reciprocally moved at a rate of .200 times/min.

When the piston rod was projected toward the filaments runningzthrough-the device, the filaments were bent'between the two guide 'rollers at a maximum distance of 10 cm. When the piston rod was returned to the original position, the filaments ran along a straight line path. -=The filaments were given periodically varying fineness by the impactings, and then wound up 'at a velocity of 8 -m./min.

The filaments were drawn in boiling water at a draw ratio "of about 5, rinsed with water and dried. 'The dried filament bundle was heat-treated at a temperature: of 130 C. to shrink'the filament bundle at a shrinkage of 30%.

The resultant filament bundle had an average total denier of 200,000. The individual filament in the resultant filament bundle had an average fineness of denier and was composed of intermittent finer portions which has an thebundle was pulled-out from the pressed were crammed into a groove of 5 cm; width, 51cm. depth and" 1 0 cm. length'and pressed at a load of 33 g./cm.

coun- TABLE 1 Treating Treating agent condition Pullout resistance (gm) Ridge Propor- Temper- Group on ature Time 00- Counter- Interval Height 0. Component (percent) 0' 0.) (mid) direction direction (a) L/ D 1 2 (ll D 5 1 Ethylene carbonate--- 90 3. 0 5. 5 5. 5 0.5 50-500 0. l2 er 2 'y-butylo- 90 2. 8 4. 4 7. l 0.3 50-500 0.12

ater 75 3... Ethylene carbon 6 Sodium sulfate... 44 95 15 2. 8 5. 7 5. 5 0. 7 50-500 0.12 Water 50 4 Ethylene carbonate.-- l0 Magnesium sultate 39 95 30 2. 9 4. 0 5.0 0. 4: 50-500 0. 12 Water 51 r 5 Ethylene carbonate 7 Manganese sulfate" 59 95 15 3.0 4. 2 7.0 0. 4 SO -500 0 12 Water 84 1 L represents length in p of tapering portion of fiber. 2 D represents an average diameter in p of middle portion of fiber. 3 d represents an average diameter in p of tapering portion of fiber.

average fineness of 1.8 clearer and length of 28 mm. and Example 2 intermittent thicker portions having an average fineness of 5.8 denier and length of 112 mm. The finer and thicker portions were distributed at random in the filament bundle. The filament bundle was supplied to a perlock system to prepare tapering staple fibers. The staple fibers thus obtained were treated in an aqueous solution containing 2% by weight of sodium hydroxide at a temperature of 90 C. for 30 minutes in order to insolubilize the fiber at the surface, and then bleached in an aqueous solution containing 2% by weight of oxalic acid at a temperature of 98 C. for 15 minutes.

The staple fiber thus treated was embedded in an embedding substance consisting of parafin and ethyl cellulose. The thicker portion of the embedded staple fiber was laterally sliced at a thickness of about 4,. The resultant slice was immersed in dimethyl formamide at a temperature of 75 C. The outer layer of the slice which was The tapering staple fibers prepared by the same procedure as that of Example 1 were divided into three groups and the groups were pretreated with the insolubilizing agents under the conditions as shown in Table 2 in order to insolubilize the fibers at the surface. The outer layers of the fibers thus pretreated had the cross-sectional areas, as shown in Table 2.

Next, the pretreated fibers were further treated in a shrinking solution consisting of 20% by weight of ethylene carbonate and 80% by weight of water in order to form the ridges on the fibers.

The resultant ridges on the fibers had asymmetrical shapes and had the intervals and heights as shown in Table 2. The ratios of the cross-sectional area of the insoluble outer layer of the thicker middle portion with respect to the whole area of the portion are also shown in Table 2.

TABLE 2 Cross-sectional Pretreatment area ratio (percent) of Ridge Concen- Temperinsoluble outer Group tration attire Time layer of thicker Intervals Height number Denaturalizing agent (percent) 0.) (min.) middle portion 1, p:

1 Sodium hydroxide. 1. 5 95 80 15 5. 5 0.5 2--.. Potassium hydroxide" 3. 0 95 30 13 7. 0 0. 4 3 Lithium. hydroxide.-- 1. 5 95 30 14 6. 9 0. 4

insolubilized by ,the above procedure, was observed by Example 3 means of a scanning-type electron microscope. It was noticed from the observation that the ratio of area of the insoluble outer layer with respect to the whole area of the slice .Was 16%.

Aquantity of the staple fibers were, divided into five groups and the groups were treated with the treating agents as shown in Table 1, respectively. The result was a tapering fiber having ridges thereon. The microscopic photo graphs of the resultant tapering fibers are shown in FIGS. 1 and 2.

In order to determine the pull-out resistance of the re 9 temperature of 50 C. consisting of 55% by weight of dimethyl acetamide and 45% by weight of water through a spinneret having 40,000 orifices of 0.06 mm. diameter to form the filaments. The coagulated filaments were rinsed with water, drawn in boiling water at a draw ratio sultant tapering fiber, the resultant staple fiber bundle of 2.5 and then dried-The dried filaments were preheated on a heating roller and then further drawn between a pair of drawing rollers at a draw ratio of 2. The device of FIG. 4 was arranged between the drawing rollers which were spaced at 60 cm. distance, and the filaments were periodically bent at a maximum distance of cm. at a rate of 200 times/min. by the device. The resultant filaments were heat treated so that the filaments shrunk about 30%. The shrunk fibers had an average fineness of 3 denier, the finer portion of the fibers had a fineness of 1.5 denier and length of about 28 mm. and the thicker portion had a fineness of 3.5 denier and a length of about 112 mm., and therefore, the intervals of the fineness variations were about 140 mm.

The filaments thus prepared were converted to tapering staple fibers by cutting them using the perlock system.

The staple fibers were insolubilized at the surface in a liquid containing 13% of hydroxyl ammonium sulfate and of sodium phosphate based on the weight of the staple fibers at a liquor ratio of 1:7 at a temperature of 120 C. for 90 minutes, rinsed with water and then dried. The staple fibers thus insolubilized had an outer layer insoluble in dimethyl formamide at a temperature of 75 C. as were similar fibers of Example 1 which were treated with an aqueous solution of sodium hydroxide. The area of the insoluble outer layer cross-section of the thicker portion of the treated fibers was 23% with respect to the whole cross sectional area of the thicker portion.

The insolubilized staple fibers were treated in a shrinking liquid consisting of 20% by weight of ethylene carbonate and 80% by weight of water at a temperature of 95 C. for minutes in order to form the asymmetrical ridges having directionality on the fiber surface. The ridges thus formed had the dimensions as shown in Table 3.

TABLE 3 Ridge Interval (a) Height L/D d/D The resultant staple fibers which had a dyeability to acid dyes were blended with the staple fibers of Group 1 in Table 2 of Example 2 which have a dyeability to basic dyes at a blend ratio of 25 :75 and the blended fibers were converted to a two-folded yarn of 2/36 meter count and twist number of 250/360 turns/meter. A plain knitting of 14 gauge was prepared from the above yarn and dyed under the following condition.

Composition of dyeing bath Percent OWF Suninol yellow R (*1) 12 Basacryl yellow SRL (*2) 0.2 Basacryl Red GL (*2) 2.0 Basacryl Blue GL (*2) 0.3

Sulfuric acid (60% conc.) 5

The tapering staple fibers prepared by the same process as that of Example 1 were insolubilized at the surface in an aqueous solution containing 20% by weight of hydrazinium sulfate at a liquor ratio of 1:7 at a temperature of 100 C. for minutes, rinsed with water and then dried. The insolubilized fiber had an outer layer insoluble in dimethyl formamide similar to fibers of Example 1 which were treated with an aqueous solution of sodium hydroxide. The cross-sectional area of the insoluble outer layer of the thicker portion of the fiber was 14% with respect to that of the whole cross-section of the thicker portion.

The insolubilized fibers were treated in a shrinking solution consisting of 8% by weight of ethylene carbonate, 42% by weight of sodium sulfate and 50% by weight of water at a temperature of 98 C. for 30 minutes. By the above treatment numerous asymmetrical ridges having directionality were formed on the fiber surface.

Example 5 A filament tow of a total denier of 60,000 and an individual filament fineness of 3 denier was prepared from a copolymer of 93% by weight of acrylonitrile and 7% by weight of vinyl acetate according to the process similar to that of Example 1.

The filament tow was subjected to draft-cutting by means of a perlock system. A heating pin which vibrates so as to intermittently contact the filament tow, was located between a front roller group and a back roller group of the system. The draft-cutting and heating of the filament tow were carried out under the following conditions.

Feed rate of filament tow: l5 m./min. Vibration number of heating pin: 50 times/min. Outside diameter of heating pin: 42 mm. Temperature of heating pin: 185 C.

Delivery rate of filament tow: m./ min.

By the above special draft-cutting, the filament tow was converted to tapering staple fibers.

The tapering fibers were insolubilized at the surface by treating with an aqueous solution containing 2% by weight of sodium hydroxide at a temperature of 90 C. for 30 minutes and bleaching with an aqueous solution containing 2% by weight of oxalic acid at temperature of 98 C. for 15 minutes.

The insolubilized tapering fibers were immersed in an aqueous solution containing 7% by weight of ethylene carbonate at 40 C. for 10 minutes, squeezed to a liquid absorption of 70% based on the weight of the fibers, and heat-treated at a temperature of 100 C. for 60 minutes using a hot air-dryer.

The resultant tapering fibers had the dimensions as shown in Table 4.

Table 4 shows that the resultant tapering fiber is within the scope of the present invention.

Staple fibers prepared by the same process as that of Example 5 were insolubilized at the surface by treating with an aqueous solution containing 13% of hydroxyl ammonium sulfate and 20% of sodium phosphate based on the weight of the fibers at a liquor ratio of 1:7 at a temperature of C. for 90 minutes, rinsed with water and then dried. The cross-sectional area of the insolubilized outer portion of the thicker portion of the fiber in dimethyl formamide was 25% with respect to the whole cross-sectional area of the portion.

The resultant staple fiber which is dyeable to acid dyes was blended with the conventional acrylic fibers which are dyeable to basic dyes and have an individualjjber fineness of 3 denier at a blend ratio of 40:60, and the blend was converted to a two folded yarn of 2/ 36 meter yarn was dyed under the following conditions.

summon snow R '1.7

Basacryl Yellow SRL 0.2 Basacryl Red GL 2.0 Basacryl Blue GL 0.3

Sulfuric acid (60% cone.) 5.0

Liquor ratio: 1:30 Temperature: 100 C. Time: 60 minutes.

The dyed yarn was impregnated in an aqueous solution containing 8% by weight of ethylene carbonate, 7% by weight of Zontes TA 430 (which is the trade mark of a softening agent made by Matsumoto Oil and Pats Co., Ltd, Japan) and 85% by weight of water at a temperature of 40 C. for 10 minutes, squeezed to a liquid absorption of 70% based on the weight of the fibers and dried at a temperature of 120 C. for 60 minutes using a hot air dryer.

The yarn was further treated with hydroxyl ammonium sulfate. By the above treatment, numerous asymmetrical ridges having directionality were formed on the fibers.

The ridges formed on the thicker portion of the fibe had intervals of 5.0a and a height of 0.7;t.

The yarn thus treated was knitted into a plain knitting of 14 gauges.

In the resultant dyed knitting, the minor yellow fibers were dispersed in the major brown fibers. The dyed knitting had a very soft hand feeling and an elegant appearance and thus, was of great commercial value.

What we claim is:

1. An improved acrylonitrile synthetic fiber consisting of a polymer containing at least 85% by weight of acrylonitrile and the remaining amount of at least one ethylenically unsaturated monomer copolymerizable with acrylonitrile, which is composed of a thicker middle portion and finer tapering end portions extending from the thicker middle portion and tapering at each end, and has dimensions satisfying the following relationships:

where D represents an average diameter in ,u. of the thicker middle portion, d represents an average diameter in a of each finer tapering end portion and L represents an average length in a of each finer tapering end portion, the outer layer of said fiber is insoluble in dimethyl formamide at a temperature of 75 C., said outer layer of said thicker middle portion has a cross-sectional area of 2 to 40% based on the whole cross-sectional area of said thicker middle portion, and is provided, on the fiber surface of said thicker middle portion, with numerous asymmetrical ridges outwardly projecting from the fiber surface at intervals of 1.5 to 12p. in a direction inclined with respect to the cross-sectional plane of the fiber and having a height of 0.2 to 1.5

2. A process of manufacturing an improved acrylonitrile synthetic fiber consisting of a polymer containing at least 85% by weight of acrylonitrile and the remaining amount of at least one ethylenically unsaturated monomer copolymerizable with acrylonitrile, which is composed of a thicker middle portion and finer tapering end portions extending from the thicker middle portion and tapering at each end, and has dimensions satisfying the following relationships:

.wherein D represents an: average diameter in ,u of the thicker rniddleportion, d'represents an average diameter m a of each finer tapering end portion and L'represents a length in ofeachfiner tapering end portion, the outer layer'of said fiber is'insoluble in dimethyl formamid'e at t'fitempe'rature'"of C. said outer layer of said thicker middle portion has a cross-sectional area of 2 to 40% based on the whole cross-sectional area of said thicker middle portion, and is provided, on the fiber surface of said thicker middle portion, with numerous asymmetrical ridges outwardly projecting from thefiber surface at in tervals of 1.5 to 12 in a direction inclined with respect to the cross-sectional plane of the fiber and having a height of 0.2 to 1.5;, which comprises spinning, to form'an acrylonitrile synthetic filament, a polymer containing 'at least 85% by weight of acrylonitrile and the remaining amount of at least one ethylenically unsaturated monomer copolymerizable with acrylonitrile and drawing said spun filament in the longitudinal direction thereof, while periodically varying the fineness of said filament along .the length thereof during said spinning or saiddrawing step, draft-cutting said filament at its finer portions into tapering staple fibers which are tapering at each end, insolu'bilizing said tapering staple fiber at its surface by treating it with an insolubilizing aqueous solution containing at least one member selected from the group consisting of hydroxides of sodium, potassium and lithium, sulfuric acid, hydroxyl amine salts and hydrazine salts, and then shrinking said insolubilized staple fiber by treating it in a shrinking aqueous solution containing at least one compound selected from organic carbonates, lactones, and maleic acid anhydride until the aforesaid fiber having the aforesaid asymmetrical'ridges is formed.

3. A process as claimed in claim 2, wherein said shrinking aqueous solution further contains at least one sulfate selected from the group consisting of sodium sulfate, potassium sulfate, magnesium sulfate, zinc sulfate, alu minium sulfate, manganese sulfate, ammonium sulfate.

4. A process as claimed in claim 2 wherein said organic carbonate is selected from the group consisting of ethylene carbonate, propylene carbonate, trimethylene carbonate, tetramethylene carbonate and 2,3-butyl carbonate.

5. A process as claimed in claim 2, wherein said lactone is selected from 'y-butyrolactone and fi-valerolactone.

6. A process as claimed in claim 2, wherein said shrinking is carried out by treating said fiber in said shrinking solution at a temperature of 70 C. or higher.

7. A process as claimed in claim 2, wherein said shrinking is carried out by impregnating said fiber with said shrinking solution and then heating said impregnated fiber at a temperature of C. or higher.

References Cited UNITED STATES PATENTS 3,728,072 4/ 1973 Orito et al 161-181 X 2,866,256 12/1958 Matlin 161181 X 3,393,083 7/1968 Go 161l79 X 3,671,381 6/1972 Hansen 161-180 3,069,222 12/1962 Hermes 8-130.1 3,423,284 1/1969 Marek et al. 161----180 X LEON D. ROSDOL, Primary Examiner H. WOLMAN, Assistant Examiner US. Cl. X.R. 

